Method and device for imaging a section of the eyeground

ABSTRACT

A device for examining for the eyeground of a patient&#39;s eye ( 1 ) has a head holder ( 3 ) for fixing the patient&#39;s head and a slit lamp unit ( 19  or  22 ). Provided on the head holder is a laterally movable lens carriage ( 9 ), in the shaft guide ( 10 ) of which a lens holder ( 11 ) can be introduced with its shaft ( 27 ) from above. For positioning the lens ( 12 ) in front of the eye ( 1 ), the lens holder is coupled in terms of movement to the microscope by means of an adapter ( 25 ) and a guide plate ( 24 ). The lens carriage, the lens holder and the adapter or the guide plate are in this case formed in such a way that the lens holder can be spatially fixed and uncoupled from the microscope with few manipulations, which makes it possible for an image of the eyeground to be formed the microscope in an optimum way.

TECHNICAL FIELD

[0001] The invention relates to a method and a device, known as a slitlamp unit, for forming an image of a rear portion of a patient's eye,with a viewing unit having a microscope and with an optical unit.

PRIOR ART

[0002] The rear portions of an eye, for example the fundus of an eye,are typically examined and an image of them is formed by a slit lampunit, with what is known as an auxiliary lens being additionallypositioned as an optical unit in front of the corresponding eye.Depending on the focal length, this auxiliary lens makes it possible toview regions of different sizes of the eyeground.

[0003] To avoid undesired movements of the patient during anexamination, the head of the patient is fixed in a head holder. Theauxiliary lens is also typically fastened to this head holder. However,in order to permit precise positioning of the auxiliary lens in front ofthe eye, this connection must be movable.

[0004] A holding means for an auxiliary lens of this type is describedin Journal of the American Optometric Association, Volume 59, Number 7,7/88. The holding means comprises a linkage which is connected by jointsand is fastened by one end to the head holder and at the other end bearsthe optical unit. The auxiliary lens must be manually positioned in thedesired position in front of the eye, the friction of the joints beingsufficient for the auxiliary lens to remain more or less in the setposition once it is let go.

[0005] However, the problem is that it is only with very greatdifficulty that the auxiliary lens itself can be manually positionedsufficiently precisely in front of the eye, even by an experienced user.For a layperson, this is virtually impossible.

[0006] A further possible way in which an auxiliary lens can bepositioned in front of the eye is described in DE 1133911. For thispurpose, a lens carriage with a shaft guide, a vertical hole, isfastened to the head holder. The carriage is laterally displaceable, butnot vertically displaceable. A matching auxiliary lens has a cylindricalshaft, which can be introduced into the shaft guide on the carriage. Asa result, the auxiliary lens is movable both laterally (by displacingthe carriage) and vertically (by displacing the shaft in the shaftguide). The holding means for the auxiliary lens itself is movablyconnected to the shaft, so that the distance of the auxiliary lens fromthe eye can also be set in the desired way. A screw on the shaft guideallows the auxiliary lens to be fixed in the latter. For easierpositioning, the auxiliary lens can also be coupled in terms of movementto the slit lamp unit.

[0007] Here, too, it is the case that manual positioning is notsufficiently precise. Moreover, the uncoupling operation is complicatedand laborious and the eyeground cannot be scanned with a light slit of aslit lamp unit.

[0008] A further problem is that, in the case of known lens holders,although the optical unit is movably connected to the lens holder, it isfixedly connected, i.e. not detachably connected. Therefore, when a lensis changed, the entire lens holder has to be exchanged.

SUMMARY OF THE INVENTION

[0009] The object of the invention is to provide a method of the typementioned at the beginning which avoids the problems existing in theprior art and, in particular, allows precise positioning of theauxiliary lens and also unhindered formation of an image of the rearportion of an eye. Moreover, it is intended that a lens holder whichallows the optical unit to be easily exchanged should be provided.

[0010] The solution achieving the object is defined in terms of themethod by the features of claim 1 and in terms of the device by thefeatures of claim 4. The method according to the invention for formingan image of the rear portions of a patient's eye using a viewing unitand an optical unit comprises at least the following steps:

[0011] a) The optical unit is coupled in terms of movement to theviewing unit, having a microscope.

[0012] b) The optical unit is positioned in front of the patient's eyein such a way that it is located between the viewing unit and thepatient's eye in a given relative position with respect to the patient'seye.

[0013] c) The optical unit is spatially fixed in relation to thepatient's eye.

[0014] d) The optical unit is uncoupled from the viewing unit whilemaintaining the spatial fixing in relation to the patient's eye.

[0015] e) By moving the viewing unit, an image of the rear portion ofthe patient's eye is formed, the viewing unit moving substantially on aplane perpendicular to the optical axis of the eye and the eyegroundbeing scanned, for example, by a light slit.

[0016] The coupling in terms of movement of the optical unit to themicroscope of the viewing unit makes it possible to position the opticalunit absolutely precisely in front of the eye to be examined by usingthe viewing unit. The position of the optical unit can be checked at anytime by the viewing unit and also corrected by displacing the viewingunit. The spatial fixing and the uncoupling of the optical unit from theviewing unit are performed in an easy and quick way, without the risk ofunwanted displacement of the optical unit. Moreover, the auxiliary lensuncoupled according to the invention does not restrict the freedom ofmovement of the viewing unit, thereby permitting unhindered formation ofan image of the rear portions of an eye with the viewing unit.Consequently, all the desired examinations can be carried out on thepatient's eye without modifying the slit lamp unit.

[0017] To achieve a viewing range which is as extensive as possible, theoptical unit is preferably positioned in front of the patient's eye insuch a way that its focus or its focal point comes to lie on the planeof the pupil of the patient's eye. In this case, the optical axes of theeye and of the optical unit generally coincide.

[0018] For easier and safer handling, the spatial fixing of the opticalunit in relation to the patient's eye is preferably performedsubstantially at the same time as the uncoupling of the optical unitfrom the viewing unit. It is intended for the fixing and uncoupling tobe performed in this case with as few manipulations as possible,advantageously of course with a single manipulation, for example bypressing a button or by actuating a lever.

[0019] When forming an image of the rear portions of an eye, the imagefield is greatly restricted by the relatively small pupillary aperture,for which reason an optical unit is placed between the viewing unit andthe eye by coupling said optical unit to the viewing unit. By uncouplingthe optical unit after its positioning, a greatly increased image fieldis achieved when forming the image of the rear portions of the eye.

[0020] The device according to the invention for forming an image of therear portions of an eye, with a viewing unit and an optical unit,comprises means for coupling the optical unit in terms of movement tothe viewing unit, means for positioning the optical unit coupled to theviewing unit between the viewing unit and the patient's eye, means forspatially fixing the optical unit in relation to the patient's eye andalso means for uncoupling the spatially fixed optical unit from theviewing unit.

[0021] For forming an image of the rear portions of an eye, a microscopeis preferably used as the viewing unit, for example what is known as aGreenough stereo microscope, as is also used for the examination ofeyes. In such examinations, the head of the patient is usually fixed inplace. The microscope can then be positioned in any way desired in frontof the eye to be examined, more or less freely movably in alldirections. What are known as auxiliary lenses, which are usuallyfastened to a lens holder, are advantageously used as the optical unit.

[0022] In the case of a preferred embodiment of the invention, thespatial fixing of the head of the patient (and consequently also of thepatient's eye) is performed in a head holder which comprises a lenscarriage which is fastened to the head holder in a horizontally movablemanner. The horizontal movement of the lens carriage substantiallycomprises a lateral displacement, so that the lens carriage, andconsequently the optical unit, can be placed according to choice infront of the left eye or the right eye of the patient.

[0023] A correspondingly formed auxiliary lens is fastened at the upperend of a lens holder to a cylindrical shaft, the shaft being dimensionedin such a way that it can be introduced into a corresponding shaft guideon the lens carriage. The shaft guide comprises, for example, avertically arranged hole on the lens carriage, into which the shaft ofthe auxiliary lens can be introduced from above.

[0024] For the coupling in terms of movement of the optical unit to theviewing unit, the device has, for example, a guide plate which isfixedly assigned locationally to the viewing unit and has a guidegroove. In other words, the guide plate exactly follows the movements ofthe viewing unit, with the guide groove running horizontally, parallelto the optical axis of the viewing unit, i.e. parallel to the viewingdirection of the head of the patient.

[0025] The coupling is achieved by the shaft of the lens holder whichhas been introduced into the shaft guide on the lens carriage beinginserted by its lower end into the guide groove. For this purpose, theguide groove and the lower end of the shaft are formed in such a waythat the shaft cannot be turned about its longitudinal axis in the guidegroove.

[0026] The shaft of the lens holder can be inserted into the guidegroove not only directly but also indirectly by means of an adapter. Forthis purpose, the adapter is formed in such a way that it can itself beinserted into the guide groove and the shaft can be inserted into theadapter.

[0027] This coupling of the lens holder and viewing unit allows thelateral and vertical movements of the viewing unit to be transferred tothe optical unit, with the distance between the optical unit and the eyeremaining unchanged. When there are movements of the viewing unit towardthe eye or away from the eye, it is merely the shaft that is displacedin the guide groove of the guide plate. The length of the shaft is madeto match the microscope, so that the optical axis of the optical unitsubstantially coincides with the optical axis of the viewing unit, whichin the case of a microscope is the axis of symmetry of the two opticalaxes of the subsystem on the left and the subsystem on the right.

[0028] The optical unit is movably connected to the shaft, for exampleby means of a jointed parallelogram, whereby the frontal distance of theoptical unit from the eye can be set in a desired way.

[0029] The optical unit can consequently be positioned in any waydesired in front of the eye to be examined.

[0030] In the case of a preferred embodiment of the invention, the guideplate, the lens holder and the lens carriage are formed in such a waythat the optical unit can be spatially fixed in the desired position infront of the patient's eye. The lens holder can be fixed in the shaftguide on the lens carriage and/or the lens carriage can be fixed on thehead holder. The fixing is performed, for example, mechanically ormagnetically.

[0031] A preferred variant for the spatial fixing of the optical unit inrelation to the patient's eye is performed mechanically by means of asleeve attached to the shaft guide of the lens carriage. The shaft ofthe lens holder is introduced through the sleeve into the shaft guideand firmly clamped in the shaft guide, for example by turning the sleevein a way known per se, for example by constricting the inside diameter.

[0032] Furthermore, the sleeve may have, for example, a ring of externalteeth, which puts a gearwheel mechanism into operation when the sleeveis turned, said mechanism activating a brake attached to the lenscarriage.

[0033] It goes without saying that the lens holder can be fixed in anydesired manner. A further possible way is, for example, to provide theshaft of the lens holder with a buckling joint and a spreadingmechanism, which is triggered by bending away the lower end. At the sametime, the brake on the guide carriage could be activated by means of alever mechanism.

[0034] A further preferred kind of spatial fixing of the optical unit isbased on magnetic forces. In this case, the lens holder and/or the lenscarriage are firmly clamped in the shaft guide or on the head holder bymeans of one or more magnets.

[0035] In order that the rear portions of the eye can be scannedunhindered with the slit lamp unit, the optical unit is uncoupled fromthe viewing unit after it has been positioned in front of the eye.

[0036] For this purpose, the lens holder, the guide plate and theadapter, if provided, are formed in such a way that the spatially fixedoptical unit can be uncoupled from the viewing unit preferably byhorizontal and/or vertical moving out or pivoting out of the lower endof the shaft, of the adapter or of the guide plate.

[0037] For the uncoupling, the guide plate is, for example, connected tothe viewing unit by means of a spring mechanism similar to the refilladvancement of a ballpoint pen. The spring mechanism allows the guideplate to be pressed down and in this way releases the shaft of the lensholder by moving out vertically. The spring mechanism is in this casepreferably formed in such a way that the guide plate engages in thisposition and can be released again by pressing once again.

[0038] Another variant consists in that the adapter, if provided, hasthe spring mechanism mentioned above. After pressing down, however, theadapter can be removed manually, for which reason the adapter does nothave to engage after the pressing together.

[0039] In the case of a further variant, the shaft of the optical unithas, for example, a joint, in particular a buckling joint (as alreadymentioned further above). The uncoupling of the optical unit from theviewing unit is performed by pivoting the lower end of the shaft outfrom the guide groove, for example by manual bending of the joint, itbeing possible, as already described, for the lens holder to bespatially fixed at the same time.

[0040] A further possible way of uncoupling the shaft from the guideplate is, for example, to form the lower part of the shaft in such a waythat it is telescopically extendable. In other words, the shaftcomprises at least two cylindrical parts which can be pushed one intothe other. The pushing of one into the other, i.e. the vertical liftingof the lower shaft end out of the guide groove, could be performed, forexample, magnetically by activation of a corresponding magnet.

[0041] It goes without saying that any desired combinations ofmechanical and magnetic fixing and uncoupling of the optical unit arepossible.

[0042] The positioning of the optical unit in front of the eye can beperformed both manually and automatically, in respect of which it goeswithout saying that mixed forms are also possible. The viewer may, forexample, perform rough positioning of the optical unit with the aid ofthe viewing unit and have the fine adjustment carried out by anautomatic positioning device before or after the uncoupling of theoptical unit from the viewing unit. Such an automatic positioning devicecomprises, for example, a pupil sensor for ascertaining the exactposition of the pupil of the eye to be examined and also a device forthe precise positioning of the optical unit in relation to the pupil. Ofcourse, in addition to the positioning, the uncoupling and fixing of theoptical unit may be performed not by the user but by a correspondingautomatic device.

[0043] In the case of a particularly preferred embodiment of theinvention, the uncoupling of the lens arrangement from the viewing unitis performed substantially at the same time as the spatial fixing of theoptical unit in relation to the patient's eye, both taking place withoutany locational displacement of the optical unit. In this case,“substantially at the same time” means that the uncoupling and fixingcan be performed by a preferably single movement on the part of theviewer, i.e. by pressing a button or actuating a lever, it beingpossible for the button or the lever to be attached at a suitable place,for example to the viewing unit, to the head holder or to the opticalunit.

[0044] For creating images of the portions of an eye to be examined, theviewing unit is preferably formed in such a way that an imageacquisition device operates together with it. For example, a videocamera or a photo camera may be connected via a corresponding cameraadapter. Digital cameras (for example CCD, CMOS) are also very wellsuited, having the advantage that the images captured can be digitallyfurther processed directly.

[0045] Appropriate forming of the camera adapter or the camera alsoallows further functions to be integrated, such as for example a zoom orfine adjustment. In this way it is possible to select an image cutout ofinterest and show it enlarged.

[0046] To permit easy and quick changing, i.e. exchanging, of theoptical unit, the lens holder is formed in such a way that the opticalunit can be firmly clamped on the lens holder and removed againmanually.

[0047] A preferred embodiment of the lens holder comprises two holdingparts resiliently connected to each other, which are arranged at aspecific distance from each other, corresponding to the thickness of theoptical unit. The optical unit can in this way be clamped convenientlyand easily between these two holding parts, and similarly be removedagain easily.

[0048] However, the use of such a lens holder is not restricted to theapplication in conjunction with the device described above. It goeswithout saying that it can be used wherever optical units, for exampleindividual lenses, have to be introduced into any desired path of rays.

[0049] Further advantageous embodiments and combinations of features ofthe invention emerge from the following detailed description and thepatent claims as a whole.

BRIEF DESCRIPTION OF THE DRAWINGS

[0050] In the drawings used for explaining the exemplary embodiment:

[0051]FIG. 1 shows a device according to the invention for forming animage of the eyeground;

[0052]FIG. 2 shows a lens holder with a lens, mounted on the guideplate;

[0053]FIG. 3 shows a cross section through the guide plate with the lensholder;

[0054]FIG. 4 shows the cross section from FIG. 3 with the guide platepressed together;

[0055]FIG. 5 shows a lateral view of a detail of the upper end of thelens holder;

[0056]FIG. 6 shows a front view of the upper end of the lens holder;

[0057]FIG. 7 shows a lens carriage with a lens holder guide;

[0058]FIG. 8 shows a view of a detail of the lens carriage from above;

[0059]FIG. 9 shows an adapter for coupling the lens holder to the slitlamp unit;

[0060]FIG. 10 shows a lateral view of a detail of the lower end of thelens holder with a buckling joint;

[0061]FIG. 11 shows a view of a detail of an electromagneticallyoperating, telescopically formed lower end of the lens holder with thecurrent switched off;

[0062]FIG. 12 shows the lens holder from FIG. 11 with the currentswitched on and

[0063]FIG. 13 shows several paths of rays for forming an image of thefundus.

[0064] In principle, the same parts are provided with the samedesignations in the figures.

[0065] Ways of Implementing the Invention

[0066] The invention is to be explained in detail below on the basis ofseveral examples.

[0067]FIG. 1 shows a slit lamp unit 14 according to the invention fromthe side, mounted on a table 13, for forming an image of the rearportions, in particular the fundus (eyeground), of the eye 1 of apatient 2. The head of the patient 2 is fixed in a head holder 3. Forthis purpose, the chin 4 and forehead 5 of the patient are resting on achin support 6 and a forehead support 7, respectively.

[0068] The chin support 6 has a rail 8, which lies perpendicularly inrelation to the image plane and in which a lens carriage 9 can be movedback and forth (perpendicularly in relation to the image plane). Thelens carriage 9 comprises a shaft guide 10, into which there has beenintroduced a lens holder 11, which bears at its upper end a lens 12, asan auxiliary lens.

[0069] Mounted on the side of the head holder 3 opposite from thepatient 2 there is a slit lamp unit 14. This comprises a cross slide 15with a steering lever 16, with the aid of which the slit lamp unit 14can be moved horizontally (for example by inclining the steering lever16) and vertically (for example by turning the steering lever 16).

[0070] In conjunction with the slit lamp unit 14, the lens 12 on thelens holder 11 can be moved freely, and of course also positioned infront of the eye 1, by lateral displacement of the lens carriage 9 andby vertical displacement in the shaft guide 10.

[0071] Furthermore, a microscope 19, for example a Greenough stereomicroscope with an optical axis 20, is fastened on a microscope arm 17,which can be pivoted about a vertically upright pivot axis 18 (here, theoptical axis 20 refers to the center perpendicular of the optical axesof the optical subsystems on the left and on the right of the microscope19).

[0072] Fastened to a lamp arm 21, which is likewise pivotable about thepivot axis 18, as a lighting unit is a slit lamp 22, the light of whichis cast via a mirror 23 into the eye 1 to be examined. To reduce oreliminate disturbing reflections of light in the eye 1, the slit lamp 22is fastened to the lamp arm 21 in such a way that it can be pivotedabout the joint 21.1 with the pivot axis 21.2 which is perpendicular inrelation to the image plane. The slit lamp 22 produces, for example, alight slit with which the eyeground is illuminated. The entire imagefield can be scanned by displacing the slit lamp unit laterally and/orvertically. In addition to the slit lamp 22, a further light source, forexample the output of a light guide, may be provided, for example on amovable arm, serving for example for lighting up the entire eyeground,while only a narrow strip of the fundus is brightly lit up by the lightslit produced by the slit lamp 22.

[0073] The device further comprises a guide plate 24, which is likewisepivotable about the pivot axis 18 and is coupled to the microscope arm17, so that it follows the pivoting movements of the latter.

[0074] On the upper side of the guide plate 24 there is a guide groove24.1 (which is not visible in FIG. 1). As a result of the rotarycoupling of the guide plate 24 to the microscope arm 17, this guidegroove 24.1 always runs parallel to the optical axis 20 of themicroscope 19.

[0075] Inserted into this guide groove 24.1 is the lower end of the lensholder 11, which has been introduced into the shaft guide 10.

[0076] In this way, the lens 12 is coupled in terms of movement to themicroscope 19 at the upper end of the lens holder 11. When there arelateral movements (horizontally, perpendicularly in relation to theoptical axis 20) and vertical movements of the microscope 19, the lens12 is made to follow the movement via the guide plate 24 and lens holder11. When there are movements forward or back in the direction of theoptical axis 20, the lens holder 11 slides forward and back in the guidegroove 24.1, without the distance of the lens 12 from the eye 1changing. To be able to set this distance, the lens 12 is connected tothe lens holder, for example, by means of a parallel joint 26.

[0077] When forming the image of the eyeground, the lens 12 consequentlylies exactly in the optical axis 20 between the eye 1 and the microscope19. As already mentioned, the lens 12 makes it possible to view a largearea of the fundus of the eye with the microscope 19, which isillustrated in FIG. 13. For the sake of simplicity, only the path ofrays for three points of the fundus 52.1, 52.2, 52.3 of the eye 1 isrepresented in FIG. 13. Respectively represented for each point of thefundus 52.1, 52.2, 52.3 are the principal ray 53.1, 53.2 and 53.3 andthe two marginal rays 53.4, 53.5, 53.6, 53.7, 53.8 and 53.9, which juststill pass through the pupil of the eye 1 to the outside. The principalrays 53.1-53.3 and the marginal rays 53.4-53.9 are refracted at thecornea, i.e. the interface between the eye 1 and the air. All the raysoriginating from a single point of the fundus of the eye run paralleloutside the eye 1 (assuming a healthy eye 1). The refraction of the raysat the crystalline lens is negligible in comparison with the refractionat the cornea and is therefore not shown. If the lens 12 were notpresent, these rays 53.1-53.9 would continue to run in a straight line(represented as dotted lines).

[0078] An image is formed by the lens 12 of all the rays of a singlepoint of the fundus 52.1-52.3 onto an image plane 56, so that an image52.4-52.6 is produced. The distance between the lens 12 and the plane ofthe pupil 55 corresponds approximately to the focal length of the lens12. In this way, the telecentric condition is satisfied and theprincipal rays 53.1, 53.2, 53.3 are all parallel to the optical axis 20in the direction of the microscope 19.

[0079] To be able to view this image in the image plane 56 with themicroscope 19, the microscope 19 just has to be focused to the imageplane 56. To be able to view or scan all the regions of the fundus, themicroscope 19 is displaced in a plane parallel to the image plane 56,without changing the distance of the microscope 19 from the image plane56 or from the eye 1. This displacement is represented by the two arrows57 and 58. Two different positions of the displaced microscope 19.1 and19.2 are depicted by dashed lines. This easy method of setting is onlypossible if the distance between the lens 12 and the plane of the pupil55 is chosen such that the telecentric condition is satisfied.

[0080] Furthermore, this displacement allows the greatest possibleluminous flux from the region of the fundus which is to be viewed to becaptured, i.e. the brightest possible image of the region of the funduswhich is to be viewed to be obtained.

[0081] To make it easier for the viewer to displace the microscope 19parallel to the image plane 56, the cross slide 15 could be provided,for example, with a kind of brake, which could be switched on after thepositioning of the lens 12 and the microscope 19. This brake would thenprovide an increased movement resistance of the cross slide 15 in thedirection toward the eye 1 (or away from it) or make such microscopedisplacements completely impossible. However, blocking of the crossslide 15 is not very advantageous, since, even with such accuratepositioning, small corrections of the distance of the microscope aresometimes necessary.

[0082] Positive lenses 12, which produce an actual image of the fundusof the eye between the lens 12 and the microscope, are preferably used,although negative lenses 12, which produce a virtual image (behind thelens 12 as seen from the microscope), can also be used.

[0083]FIG. 2 shows the lens holder 11 and the guide plate 24 on a largerscale. The lens holder 11 comprises a shaft 27 and, at the upper end ofthe latter, the parallel joint 26. This comprises a linkage which isformed in the manner of a parallelogram and the sides of which areconnected to one another in a jointed manner. One side of theparallelogram is perpendicular in relation to the shaft 27 and is firmlyconnected to the upper end of the latter. Connected to the side parallelto the latter side is a clamping device 28, into which the lens 12 canbe firmly clamped on the lens holder 11 and removed again manually in aneasy manner. This is particularly helpful if the lens 12 is to beexchanged for another lens during the examination. For changing thedistance of the lens 12 from the eye 1, one of the other two sides islengthened and forms an adjusting lever 29.

[0084] In FIGS. 3 and 4, a longitudinal section through the lower end ofthe shaft 27 and the guide plate 24 is represented. Formed at the lowerend of the shaft 27 is an adjusting spring 30, which is fitted in aguide groove 24.1 of the guide plate 24. The adjusting spring 30 extendsover the entire width of the shaft 27 and lies parallel to the opticalaxis of a lens 12 mounted on the lens holder 11.

[0085] The guide plate 24 comprises a lower part 24.2 and an upper part,which comprises a plate 24.4 with the guide groove 24.1 and a kind ofhollow cylinder 24.3, which is attached on the underside of the plate24.4. The outside diameter of the lower part 24.2 is smaller than theinside diameter of the hollow cylinder 24.3. Both are formed in such away that the lower part 24.2 can be pushed into the hollow cylinder 24.3from below.

[0086] A helical spring 44 is fastened between the upper part and thelower part 24.2 in such a way that the parts pushed one into the otherare pressed apart. In order that the two parts do not cant when they arepushed one into the other or pushed apart, fitted inside the hollowcylinder 24.3 is a guide pin 45, which is guided in a guide bore 46.1 onthe lower part 24.2. The guide bore 46.1 is used at the same time forguiding the helical spring 44. In order that the upper part and lowerpart 24.2 are not pressed too far apart by the helical spring 44,provided in the lower part 24.2 is a further guide bore 46.2, throughwhich a screw 47 is screwed from below into the plate 24.4 of the upperpart. The head of the screw 47 serves as a stop, in order that thehollow cylinder 24.3 and the lower part 24.2 do not fall apart. Thescrew also serves at the same time for improving the guidance of thelower part 25.2 in the hollow cylinder 24.3.

[0087] The upper part has on its upper side a guide groove 24.1, intowhich the adjusting spring 30 of the shaft 27 can be fitted. The guidegroove 24.1 extends continuously over the entire length of the guideplate 24, so that the shaft 27 inserted into the guide groove 24.1 ishorizontally movable in the direction of the guide groove 24.1. Asalready mentioned, the guide plate 24 itself is connected to themicroscope arm 17 pivotably about the pivot axis 18, so that it followsa pivoting movement of the microscope arm 17.

[0088]FIG. 3 shows the cross section through the guide plate 24 in thepressed-apart state, i.e. with the helical spring 44 relaxed (more orless) and the shaft 27 of the lens holder 11 inserted. FIG. 4, on theother hand, shows the guide plate 24 in the pressed-together state. Thehelical spring 44 is compressed and the shaft 27 (fixed in the guide 10on the lens carriage 9) is no longer inserted in the guide groove 24.1.By pressing together, the shaft 27 is released and the lens holder 11 orthe lens 12 is consequently uncoupled in terms of movement from theguide plate 24 and from the microscope 19.

[0089] By means of a fixing mechanism which is not represented, theguide plate engages, for example in the pressed-down position, andreleases the adjusting spring 30 of the lens holder 11 (in a way similarto when a refill of a ballpoint pen is fixed in the writing position ortransporting position). After that, the desired examinations can becarried out, it being possible for the guide plate 24 also to be removedcompletely beforehand to increase the freedom of movement of the slitlamp unit. By replacing the guide plate 24 and pressing it once again,the arrestment is released, for example, and the guide plate is back inthe original position.

[0090]FIGS. 5 and 6 show a cross section and a frontal view of theclamping device 28 with a mounted lens 12, which is held in a lens mount12.1 and fastened to the parallel joint 26. The clamping device 28comprises a base 31 and also a front holding part 32.1 and a rearholding part 32.2, which are fastened at a specific distance from eachother on the base 31. The distance between the two holding parts 32.1and 32.2 on the base 31 is either fixed by being made to match thethickness of a specific lens or the width of the lens mount or can bevariably set. Moreover, the two holding parts 32.1 and 32.2 are formedin such a way that the distance between them become smaller as thevertical distance from the base 31 increases.

[0091] The base 31 and/or the holding parts 32.1 and 32.2 consist of anelastic material, in order that a lens 12 which has a lens mount 12.1which is wider than the smallest distance between the two holding parts32.1 and 32.2 can be clamped between the latter.

[0092] To increase the spring action of the holding parts 32.1 and 32.2,a slot 33 is formed in the base 31.

[0093] In FIG. 7, the chin support 6 with the lens carriage 9 running inthe rail 8 is represented from a lateral view. The lens carriage 9 runson a plurality of rollers 34.1, 34.2, 34.3 and 34.4. The shaft guide 10on the lens carriage 9 comprises a knurled screw 35 (which may also beconfigured just as a sleeve), which has a ring of teeth 36 at its lowerend. By turning the knurled screw 35, on the one hand [sic] the shaft 27of a lens holder 11 introduced into the shaft guide 10 is firmly clampedin the shaft guide 10. This takes place, for example, in a known mannerby means of reducing the inside diameter of the shaft guide 10.

[0094] Also provided on the lens carriage 9 is an eccentric 38, which ispivotably mounted about a pivot axis 37 and has a further ring of teeth39, which is not completely formed and the teeth of which engage in thering of teeth 36 of the shaft guide 10. By turning the knurled screw 35,consequently not only is the shaft 27 firmly clamped but the eccentric28 is also additionally turned about the pivot axis 37. On the eccentric38 there is an elevation 40, which is made by the turning of theeccentric 38 to come to lie under the roller 34.1 and block the latter,for example by pressing it against the rail 8. As a result, the movementof the lens carriage 9 in the rail 8 is braked or completely blocked.

[0095] A further possible way of blocking the lens carriage 9 in therail is that an outer edge of the eccentric 38 is formed in such a waythat its pivoting has the effect that it is pressed against the rail 8.

[0096] In FIG. 8, which shows the lens carriage 9 (at least partly),seen from above, with the shaft guide 10 and part of the rail 8, aspecial form with a bulge 41 of the eccentric 38 is represented by wayof example. In the non-blocking position (solid lines), the bulge 41 islocated at a specific distance from the rail 8, so that the lenscarriage 9 can be displaced laterally in any way desired. If the knurledscrew 35 is turned clockwise, the bulge 41 moves closer to the rail 8,until it finally touches it and is pressed against it (dotted lines).The lens carriage is blocked as a result.

[0097] Instead of forming the guide plate 24 in such a way that it canbe moved out of the shaft 27 by pressing together, an adapter 25, asshown in FIG. 9 in a perspective representation, may also be used. Theadapter comprises an upper part 25.1, a kind of hollow cylinder with acover, and a lower part 25.2, the outside diameter of which is smallerthan the inside diameter of the upper part 25.1. Both are formed in sucha way that the lower part 25.2 can be pushed into the upper part 25.1from below. The upper part 25.1 in this case corresponds to the hollowcylinder 24.3 and the lower part 25.2 corresponds to the lower part 24.2of the guide plate 24 from FIGS. 3 and 4. The upper part 25.1 has on itsupper side a groove 24, into which the adjusting spring 30 of the shaft27 can be fitted. However, the groove 42 is not continuous, so that theshaft 27 inserted into the adapter 25 is completely fixed horizontally.The lower part 25.2 of the adapter 25 has on its underside an adjustingspring 43 fitting exactly into the guide groove 24.1 of the guide plate24.

[0098] In the adapter 25 there is the same mechanism as FIGS. 3 and 4show for the guide plate 24. This form of the adapter 25 allows it to beinserted with its adjusting spring 43 into the guide groove 24.1 of theguide plate 24 and the adjusting spring 30 of the shaft 0.27 of a lensholder 11 which has been introduced into the shaft guide 10 to beinserted into the groove 42 of the adapter 25. In this way, the lens 12fastened to the lens holder 11 is coupled in terms of movement to themicroscope 19.

[0099] For fixing the lens holder 11 after positioning in front of theeye 1 of the patient 2, the knurled screw 35 is turned clockwise. As aresult, on the one hand the lens holder 11 is firmly clamped in theshaft guide 10 and, via eccentric 38, on the other hand the lenscarriage 9 is firmly clamped in the rail 8 of the chin support 6.

[0100] The uncoupling of the lens holder 11, and consequently of thelens 12, from the microscope 19 while retaining the spatial fixing isperformed by pressing the upper part 25.1 of the adapter 25 downward. Asa result, the adjusting spring 30 of the lens holder 11, which hadpreviously been inserted in the groove 42 of the upper part 25.1, isreleased (see also FIG. 4). After that, the adapter 25 itself can beremoved from the guide plate 24 by horizontal displacement in the guidegroove 24.1. (An arrestment in the pressed-together position is notabsolutely necessary in this example.)

[0101]FIG. 10 shows a further example of the shaft 48 of a lens holder11. The lower end of the shaft 48 with the adjusting spring 30 isconnected to the rest of the shaft 48 by means of a buckling joint 49.The buckling joint 49 is formed such that it can be arrested both in theextended position (solid lines) and in the bent-around position (dottedlines). The bending around of the end of the shaft is performed in thelongitudinal direction of the adjusting spring 30, i.e. the pivot axisof the buckling joint is perpendicular to the image plane. This allowsthe spatially fixed lens holder 11 to be uncoupled in terms of movementfrom the microscope 19 by simply bending around the lower end of theshaft.

[0102] It goes without saying that it is also possible to realize notonly the uncoupling but also the spatial fixing of the lens holder 11 bybending around the end of the shaft. For example, when the lower end ofthe shaft 48 is bent around, the knurled screw could be turned by meansof a lever mechanism located in the interior of the shaft 48, or amechanism for fixing the lens holder 11 in the shaft guide 10 and alsofor fixing the lens carriage 9 in the rail 8 is [sic] actuated directly.

[0103]FIGS. 11 and 12 show a further example of the configuration of theshaft 50 of the lens holder 11. The shaft 50 is of a two-partconfiguration. It comprises an upper part 50.1, formed as a hollowcylinder, and a cylindrically formed lower part 50.2, the outsidediameter of the lower part 50.2 being smaller than the inside diameterof the upper part 50.1. The lower part 50.2 is produced frommagnetizable material and has in turn at its lower end the adjustingspring 30. On the inner side of the upper part 50.1, an electricalconductor is wound up spirally to form a coil 51, the ends of which areconnected in an electrically conducting manner to an electrical powersupply (not represented). The power supply comprises, for example, abattery in the upper part 50.1 of the shaft 50. The supplying of thepower may also take place from an external power supply, for example viaguide plate 24, via lens carriage 9 or via freely routed cables.

[0104] If, for example, by pressing a button, a constant electricvoltage is applied to the ends of the conductor of the coil 51, amagnetic field is generated in the interior of the coil 51, pulling thelower part 50.2 of the shaft 50 into the coil 51 and consequentlypulling it upward.

[0105] It goes without saying that fixing of the lower part 50.2 in thepulled-in and/or moved-out position may also be provided. Or the lowerpart 50.2 is formed as a magnet, for example as a bar magnet, and ispulled upward or pressed downward by switching on the current.Furthermore, there may also be tension springs or compression springs,which move the lower part 50.2 back into the original position againafter deflection by the magnetic field.

[0106] Here, too, the fixing of the shaft 50 in the shaft guide 10and/or of the lens carriage 9 in the rail 8 may be performed in variousways: either mechanically in the way already presented, by the knurledscrew being turned by the pulled-up lower part 50.2 of the shaft, orlikewise magnetically, by for example a movably mounted part of the lenscarriage 9 being pulled toward the lens holder 11 by the generatedmagnetic field and the lens holder and lens carriage fixed in this way.

[0107] A further kind of magnetic fixing is performed for example by amagnet being introduced into a magnetic circuit by the bending around ofthe lower end of the shaft 48 from FIG. 10 and said circuit being closedas a result. The magnetic circuit runs, for example, from the lensholder 11 via the shaft guide 10 and lens carriage 9 to the rail 8 andback again to the lens holder 11. The fixing could be performed, forexample, by exploiting the fact that, after the closing of the magneticcircuit, the magnetic forces attempt to reduce the magnetic resistance,in that moving parts of the magnetic circuit are minimally displaced(i.e. the corresponding air gaps are reduced) and in this way firmlyclamp the lens holder and the lens carriage.

[0108] To sum up, it can be stated that the device according to theinvention allows an image of the rear portions of an eye to be formed inan optimum way, in that the auxiliary lens which is necessary for theimage formation can be positioned with the aid of the microscope veryprecisely in front of the eye to be examined, and spatially fixedthereafter in an easy way, and can be uncoupled from the microscope inthe same working step. The examination is subsequently performed withthe freely movable microscope.

1. Method for forming an image of a rear portion of a patient's eye (1),with a viewing unit (19) and an optical unit (12), characterized in thatit comprises at least the following steps: a) the optical unit iscoupled in terms of movement to the viewing unit, b) it is positioned infront of the patient's eye in such a way that it is located between theviewing unit and the patient's eye in a given relative position withrespect to the patient's eye, c) the optical unit is spatially fixed inrelation to the patient's eye, d) the optical unit is uncoupled from theviewing unit while maintaining the spatial fixing in relation to thepatient's eye, e) by moving the viewing unit, the rear portion of thepatient's eye is viewed or an image of it is formed.
 2. Method accordingto claim 1, characterized in that the optical unit is positioned infront of the patient's eye in such a way that a focus of the opticalunit comes to lie on a plane of the pupil of the patient's eye. 3.Method according to claim 1 or 2, characterized in that the spatialfixing and the uncoupling of the lens arrangement are performedsubstantially at the same time.
 4. Device, in particular a slit lampunit, with a viewing unit and an optical unit for forming an image of arear portion of a patient's eye, characterized by means for coupling theoptical unit in terms of movement to the viewing unit, means forpositioning the optical unit coupled to the viewing unit between theviewing unit and the patient's eye, means for spatially fixing theoptical unit in relation to the patient's eye and also means foruncoupling the spatially fixed optical unit from the viewing unit. 5.Device according to claim 4, characterized in that the viewing unit is amicroscope (19), for example a Greenough microscope, and the opticalunit is an auxiliary lens (12).
 6. Device according to claim 4 or 5,characterized in that it has a head holder (3) for the locational fixingof a patient's head and consequently of the patient's eye and the meansfor coupling the optical unit to the viewing unit have a lens carriage(9), which is fastened to the head holder in a horizontally movablemanner, a lens holder (11) with a shaft (27) and also a guide plate(24), which is fixedly assigned locationally to the viewing unit and hasa guide groove (24.1), the optical unit being fastened to the lensholder and the shaft being able to be introduced into a correspondingshaft guide (10) on the lens carriage and positioned in relation to thefixed patient's eye, and the optical unit being able to be coupled interms of movement to the viewing unit by inserting the lower end of theshaft which has been introduced into the shaft guide on the lenscarriage into the guide groove, it being possible in particular for theshaft to be inserted into the guide groove securely to prevent twisting,directly or by means of an adapter (25).
 7. Device according to claim 6,characterized in that the lens holder can be spatially fixed in theshaft guide on the lens carriage and/or the lens carriage can bespatially fixed on the head holder mechanically or, preferably,magnetically.
 8. Device according to claim 7, characterized in that theshaft guide on the lens carriage has a sleeve (35) with a ring ofexternal teeth (36), it being possible by turning of the sleeve for aclamping mechanism for firmly clamping the shaft in the sleeve to beactuated and/or for a brake for firmly clamping the lens carriage on thehead holder to be activated via the ring of external teeth.
 9. Deviceaccording to one of claims 6 to 8, characterized in that the lensholder, the guide plate and the adapter, if provided, are formed in sucha way that the spatially fixed optical unit can be uncoupled in terms ofmovement from the viewing unit by horizontal and/or vertical moving outor pivoting out of the lower end of the shaft, of the guide plate or ofthe adapter.
 10. Device according to claims 4 to 9, characterized inthat it is formed in such a way that the optical unit can be uncoupledfrom the viewing unit and spatially fixed in relation to the patient'seye substantially at the same time and without any locationaldisplacement.
 11. Device according to one of claims 4 to 10,characterized in that an image acquisition device, in particular a photocamera, a video camera or a CCD camera, for recording images of the rearportion of an eye can be connected to the viewing unit.
 12. Lens holder,in particular for a device according to one of claims 4 to 11,characterized in that an optical unit can be mounted on the lens holderand removed again manually.
 13. Lens holder according to claim 12,characterized in that it has two holding parts (32.1, 32.2) resilientlyconnected to each other, between which the optical unit can be clamped.